Molding body for the production of cavities

ABSTRACT

A molding body for the production of a cavity in a metal casting such as a piston of an internal combustion engine, the molding body being composed of calcium silicate fibers held together in a solid form by a soluble binding agent.

FIELD OF THE INVENTION

[0001] The invention relates to a molding body for the production of cavities in metal castings.

BACKGROUND

[0002] The use of molding bodies, which are formed as sand cores or salt cores for the production of cavities in a cast metal body is known. After the casting of the body, the core is flushed out to form the cavity.

[0003] Such a sand or salt core is expensive to produce and requires a certain amount of time for solidifying after it has been shaped. Accordingly, these cores are very rigid, so that the danger exists that they can break apart when used in a casting mold.

DESCRIPTION OF THE INVENTION

[0004] An object of the invention is to provide a molding body for the production of cavities which avoids the described disadvantages. In addition, a particularly advantageous application of such a molding body is in the casting of pistons or other components of an internal combustion engine.

[0005] The object is achieved according to the invention in that the molding body is comprised of calcium silicate fibers, which are held together in solid form by a water soluble binding agent. The calcium silicate fibers are mixed with the water soluble binding agent and, compressed to form the molding body. The molding body can be produced in a rapid and simple manner in this way. In addition, the use of calcium silicate fibers has the advantage that these fibers are sufficiently heat-resistant and can resist a temperature of molten casting metal.

[0006] A basic advantage of the invention is that, due to the use of fibers, the cohesion of the molding body is substantially better than for conventional salt or sand cores whereby the molding bodies according to the invention are more resistant to breakage during handling when placed in the casting mold. The use of a soluble binding agent is advantageous, since the molding body must be flushed out after the casting of the body. Due to the properties of the calcium silicate fibers, the flushing out process is essentially simpler and more rapid than in the case of the cores of the prior art.

[0007] A feature of the invention is that the binding agent is formed as an inorganic binding agent soluble in water. This has the advantage that the inorganic binding agent binds very well with the calcium silicate fibers and contributes to the strength of the molding body formed therefrom.

[0008] A further feature of the invention is to mix aluminum oxide particles or powder with the calcium silicate fibers. The aluminum oxide particles or powder are of a size less than 0.2 mm and are present in an amount of 50 to 58% by weight in the composition, preferably 54% by weight. The cohesion of the molding body that is produced in this way is also further improved and attains an overall smother surface.

[0009] A novel and advantageous use of the molding body is obtained in the production of cavities in structural components of internal combustion engines. In these components, a complex casting shape is frequently required, which can only be accomplished at high cost with the conventional salt or said cores of the prior art. The molding bodies according to the invention comprised of calcium silicate fibers can be brought to the desired shape in a simpler manner for the production of the cavity. Even in the case of a greatly extended cavity (for example, cavities in an engine block of an internal combustion engine, through which cooling water is intended to flow) can be flushed out in an essentially more rapid and simpler manner, so that the production will be simplified thereby.

[0010] A particularly preferred application of the molding body according to the invention is in the production of cavities in pistons of internal combustion engines. In particular, cavities are necessary in the bottom region of the piston, these cavities being formed either as cooling channels for cooling the region at the bottom of the piston and/or to reduce the weight of the piston. Pistons of internal combustion engines are usually produced by means of a two-part or multi-part casting mold. The lower part of the piston, which is turned away from the bottom region of the piston, has for example, the crankshaft bore formed by an appropriately shaped casting core. If the finished piston is to have a cooling channel or a cavity for weight reduction, the salt or sand core is attached to so-called “center sleeves” on the casting core. The danger exists with these cores that the salt or sand core will break apart due to its rigidity. Thus, the molding body comprised of calcium silicate fibers is essentially better suitable, since it also has the required rigidity, but does not break apart, if by chance it has not been precisely introduced into position on the casting core or if it has fallen to the ground, for example, when being inserted. It is also basically simpler to flush out the molding body after the casting of the piston, in order to allow the cavity to be formed. Therefore, the molding body can also be configured in such a way that the cavity comprises, for example, not only the cooling channel alone, but also inlets and outlets therefor.

[0011] In the preferred embodiment of the invention, the calcium silicate fibers can be those produced under the trademark Lapinus 702K2-Roxul 1000. The fibers have a diameter of between 5.5 and 9.0 microns and have a specific surface area of 0.20 m²/g. The fibers have a melting point in excess of 1000° C. The fibers have a specific density between 2.5 and 3.0 g/cm³.

[0012] The fibers are present in the composition of the molding body in an amount of between 19.5 and 26.5% by weight to provide the requisite strength of the molding body to permit it to be handled (self-supporting property) without breakage and to have suitable impact strength to resist breakage if dropped on the floor.

[0013] In a particular embodiment, calcium silicate fibers (Lapinus 702K2-Roxul 1000) are present in an amount of 23% by weight in an inorganic binding agent constituted by waterglass (sodium silicate dissolved in water) sold under the trademark Silica sol. The composition is then compressed to form the molding body. 

What is claimed is:
 1. A molding body for the production of a cavity in a metal casting, said molding body comprising calcium silicate fibers held together in a solid form by a soluble binding agent.
 2. The molding body of claim 1, wherein said binding agent is an inorganic binding agent soluble in water.
 3. The molding body of claim 2, further comprising aluminum oxide mixed with the calcium silicate fibers.
 4. The molding body of claim 3, wherein the inorganic binding agent is waterglass, the calcium silicate fibers being present in an amount of between 19.5 and 26.5% by weight, and the aluminum oxide being present in an amount of between 50 and 58% by weight.
 5. The molding body of claim 5, wherein the molding body is used for producing a cavity in a structural component of an internal combustion engine.
 6. The molding body of claim 4, wherein said structural component is a piston. 